GLOBAL CORAL REEF ALLIANCE WHITE PAPER:
Nutrient analysis for integrated water quality management in tropical coastal waters
Thomas J. F. Goreau
NOTE: This White Paper consists of two parts: the first, INTEGRATED NUTRIENT MANAGEMENT OF COASTAL WATERS AND WATERSHEDS was originally published in T. J. Goreau, L. Gibby, K. Hill, A. Binger, & S. Nielsen (Editors), 2014, The Green Disc, New Technologies for a New Future: Innovative Methods for Sustainable Development, 64 chapter, 1833 pages on innovative and underutilized practical problem solving technologies, Gibby Media. The second, NUTRIENT ANALYSIS FOR EFFECTIVE COASTAL ZONE WATER QUALITY MANAGEMENT IN TROPICAL CORAL REEFS, was prepared as a strategy information briefing on April 13 2025 for the Cayman Islands Government Department of Environment.
INTEGRATED NUTRIENT MANAGEMENT OF COASTAL WATERS AND WATERSHEDS
INTRODUCTION
The fundamental problem of coastal zone management is controlling eutrophication, massive blooms of weedy algae that proliferate whenever nutrients, especially nitrogen and phosphorus, get too high (Nixon, 1995). No coastal zone manager can now adequately assess nutrient problems, design specifically targeted measures to reduce their impacts, or verify if these are working, because they lack detailed data on the locations, magnitudes and changes of coastal nutrient sources. New technology exists to allow continuous real time mapping of nutrients, identify every source, and track each to its origin. Though this technology could lift coastal zone management out of the dark ages and place it on a scientifically-sound basis, it is not now being used for this purpose.
Major obstacles to scientifically-sound coastal zone nutrient management include lack of ecosystem-specific water quality standards adequate to protect marine habitats from eutrophication, failure to use new technologies to recycle waste nutrients on land on the scale needed, inadequate assessment tools to manage watershed water quality on an integrated basis before polluted waters enter the coastal zone, and lack of methods to map coastal zone nutrient inputs in a way that allows managers to identify the major sources, reduce them, and assess success of such measures. This paper discusses new approaches to resolving these problems and restoring coastal water quality and fisheries habitat.
HARMFUL ALGAL BLOOMS
Harmful algal blooms (HABs) have greatly expanded in frequency and extent in recent years (National Academy of Sciences, 2000; Anderson et al, 2002; Hallegraeff et al., 2003; Sellner et al., 2003; Backer and McGillicuddy, 2006). They are now appearing in locations where they had not been previously documented, especially in developing countries. HABs include many different algae types. The major focus has been on “Red Tides”, blooms of single-celled “phytoplankton” algae so dense that they color the water, and frequently release toxins that can sicken or kill fish, shellfish, marine mammals, and humans. Some blooms from land based sources of nutrients can be so dense that, after they die and rot, the decomposing bacteria use up all the oxygen in the water, causing large scale death of fishes and bottom organisms due to a lack of oxygen and from hydrogen sulfide poisoning. This is the cause of “Dead Zones”, which are expanding worldwide (UNEP, 2006). Global warming will make them worse, since oxygen is less soluble in warmer water (Nelleman et al., 2008). Another equally serious, but often neglected, form of HABs are comprised of large “benthic” algae attached to the bottom, which smother and kill coral and oyster reefs and destroy fish habitat (Littler et al., 2006). Though the origins of HABs are complicated, relating for instance to interactions with other organisms in the water, or weather and ocean circulation changes, the major cause is regarded as increases in land-based sources of nutrient pollution (Howarth et al; 2000).
The growth rate of algae, like all plants, is fundamentally limited by available nitrogen and phosphorus. When these critical nutrient elements increase, they serve as fertilizers, promoting rapid growth of the weeds able to take them up fastest. These weeds smother all the other organisms in the ecosystem, causing catastrophic crashes of biodiversity and of economically valuable living resources such as coral reefs, fish, and shellfish.
Increased land-based sources of nutrients are the major factor driving coastal eutrophication. Their impact depends on circulation of coastal waters, being highest in stagnant waters, and lowest where there is strong mixing from tidal currents. The change-over can be sudden. For example, Kingston Harbour, Jamaica had coral reefs until the early 1970s. Due to cumulative impact of sewage buildup, deeper waters of the harbor suddenly went completely anoxic (Wade et al., 1972), wiping out a highly diverse bottom ecosystem first described only the year before (Wade, 1972), and never recovering. The nutrient increases in rivers and most coastal zones are so great that the resulting algal blooms and their subsequent decomposition, which removes oxygen from the water, are creating large Dead Zones that wipe out fisheries (UNEP, 2006). That of the Mississippi River discharge area into the Gulf of Mexico is best known, but there are increasing examples world wide, with some of the worst cases now appearing along the coasts of China and Europe.
COASTAL ZONE NUTRIENT SOURCES
Coastal nutrients have four major sources: oceanic, recycled, local, and land-based. Oceanic sources are derived from upwelling of deep, cold, nutrient-rich offshore waters. Humans affect this source only insofar as human-caused climate change alters global ocean circulation. There is strong evidence from global sea surface temperature studies that global changes in ocean circulation are underway, and in particular that there have been sudden, severe, extensive, and prolonged changes in upwelling that are causing many of the most productive global fisheries in these zones to collapse from the bottom up (Goreau et al., 2005). Mapping of algae in the Turks and Caicos Islands shows highly localized and persistent upwelling zones that provide significant, and previously unrecognized, nutrient backgrounds (Goreau et al., 2008). Without detailed studies of these nutrient sources it is hard to know how they are changing. Such studies are starting in the Florida Keys but are absent in other warm water coastal zones.
Recycled sources are derived from the internal cycling of nutrients from decomposition in water and underlying sediments. Humans alter these directly by building causeways and breakwaters that block water circulation, causing water to go stagnant, trapping nutrients, and increasing their release to the water from underlying sediments. This happens mainly in port areas. Large scale trawling of coastal shelves for shrimp causes major inputs of nutrients and turbidity from sediments, affecting coral reefs down-current in the Great Barrier Reef. Little research has been done on this, although the effects are visible from spacecraft photographs. Changes in global temperature and ocean circulation are also certainly altering coastal nutrient recycling, but these effects are largely unstudied and still poorly known. Decomposition of land-based sources of organic matter (from soil erosion and agricultural wastes) also cause oxygen to be removed from the water by decomposing bacteria, increasing sediment nutrient release in “Dead Zones”. A classic example of human alteration of recycling is in the Chesapeake Bay in the United States. Large oyster reefs used to filter all the water every few days, moving suspended sediment to the bottom. Sunlight could penetrate the clear water, promoting growth of bottom algae on which blue crabs fed. When oyster reefs were destroyed by overfishing, the filtration stopped, and the exchange time of water by natural currents, months long, allowed sediments to build up in the water, blocking sunlight, wiping out bottom algae and blue crabs, and causing nutrient buildup and toxic algae blooms (Newell, 1988).
Local sources here refer only to human caused inputs directly into the water from non-land based sources, from ships and marine platforms. Since there is neither mandated storage of ship sewage, nor adequate shore facilities to receive and treat it, almost all ships dump sewage and garbage at sea, usually out of sight of port. This can cause serious local pollution in harbors. In anchorages, it is clearly visible, for example, in many popular yacht anchorages, where the water is definitively greener, and the bottom algae more prolific, than in similar sites where boats don’t moor. On a global scale these sources are fairly modest and confined to localized sites, where they clearly need to be controlled by local management measures. Where these are enforced there is no sign of local pollution; for instance, the yacht mooring area of Trellis Bay in eastern Tortola, British Virgin Islands, is free of weedy algae because boats obey local ordinances to have sewage holding tanks, which must be emptied only outside the bay in open sea water. In contrast, at yacht anchorages in the Tobago Cays, in the St. Vincent Grenadines, the bottom is covered with green algae indicating very high nutrients, which are not found outside anchorage areas. Cruise liner anchorage areas in Cozumel, Mexico, don’t have locally higher weedy algae because the big ships dump their sewage at sea, not in port. Since land-based sewage is pumped to the far north of Cozumel, the major source of nutrients in that area can be clearly mapped to come from excrement and rotting food from captive dolphin pens (Goreau, 2006).
Land based sources of nutrients are the major mechanism by which humans most strongly and directly alter coastal water quality. There are at least six major mechanisms leading to increased nutrient flows to the coastal zone. 1) Human sewage; Most human sewage is untreated and goes directly into surface and ground water. Very little of what is treated reaches levels where nutrients are removed. These accumulate in the liquid effluents discharged to the environment via surface water, ground water, or ocean sewage outfalls 2) Agricultural wastes; Very little livestock manure is treated at all, nor are the nutrients from crop residues. 3) Fertilizer; The amounts of nitrogen, phosphorus, and other nutrients applied to soils are steadily increasing, and due to their highly inefficient over-use, only a small part of the nutrients are actually taken up by the crops, with the rest flowing into ground water and streams. 4) Air pollution; Combustion of fossil fuels leads to production of large amounts of nitrogen oxides that dissolves and falls out in rainwater, much of it over coastal zones. In addition fertilizer ammonium volatilization adds to rainwater nitrogen loading. 5) Ground water contamination; Ground waters are increasingly unusable for drinking because of contamination with high levels of nitrogen and other pollutants. Much of this is discharged to the coastal zone via recharge of rivers, but in coastal zones there is significant flow of groundwater to the ocean, especially in high, wet areas. Limestone formations are especially permeable and release large amounts of groundwater to the ocean, especially on high wet islands like Jamaica. Due to the high pH of limestone soils, these discharges have extremely high levels of nitrate, but often low phosphorus levels (Goreau & Thacker, 1994). 6. Soil erosion; Increased deforestation, poor agricultural land management, and urbanization result in increased erosion of soils, which dumps soil nutrients into coastal waters.
ECOSYSTEM SPECIFIC WATER QUALITY STANDARDS
To protect coastal ecosystems from eutrophication, scientifically-sound nutrient water quality standards are needed. At this point no country in the world has any. Water quality standards have historically been developed for human public health, not ecosystem health, and reflect the limits above which people get sick. There are no public health limits for phosphorus, and for nitrate the usual standard is 10 parts per million (ppm). Above this, babies can get methemoglobinemia, or “blue baby syndrome”, in which the nitrate binds to blood hemoglobin oxygen receptors and babies effectively suffocate.
However, coral reefs become algae dominated if available phosophorus (orthophosphate plus dissolved organic phosphorus) is above 0.003 ppm, or if available nitrogen (nitrate, nitrite, plus ammonium) is above 0.014 ppm (Bell, 1992; Lapointe et al., 1993) See Figure 1 and 2. Corals will die from algae overgrowth at nitrogen levels around 700 times lower than what we can safely drink! Other marine ecosystems also have eutrophication nutrient limits, but they are all much higher than coral reefs; for seagrasses they are 30-50 times higher than for coral reefs (Lapointe et al., 1994). Saying that water is “clean” because people don’t die from it does not protect ecosystems that are affected at much lower levels. Effective coastal zone management requires development and enforcement of ecosystem-specific water quality standards. The Turks and Caicos Islands in the Caribbean are the only country in the world so far to propose adopting water quality standards that could protect their coral reefs.
FIGURE 1. Algae covered reef, in which around 95% of the corals have been killed and overgrown by weedy algae. Oracabessa, Jamaica, 2009. Photograph by Andrew Ross
FIGURE 2. Coral dying back from Yellow Band Disease as algae overgrows it. Discovery Bay, Jamaica, 2009. Photo by Thomas J. Goreau.
SEWAGE TREATMENT AND NUTRIENT RECYCLING
Because nutrient rich land-based surface and groundwater runoff are killing coral reefs and fisheries in expanding areas around all populated tropical coastal areas, it is crucial that all these nutrients be recycled on land and prevented from entering coastal waters (Goreau, 2003). Why overfertilize the water and kill our most productive coastal resources when the land is short of nutrients for agriculture (which are provided by costly fertilizers), and while agriculture and human populations are increasingly running short of fresh water? Until recently sewage was regarded as waste, to be dumped in water or into the ground as fast as possible. Now we recognize that water and nutrients are both scarce and valuable resources that need to be recycled. It is no longer cheaper to throw them away. Until recently, treating wastewater to remove nutrients was very costly and required large areas to dry sewage sludge. In addition the level of treatment applied, which aimed at protecting human health by removing disease-causing bacteria and parasites, did not remove the vast bulk of the nutrients, which were discharged to the environment in “waste waters”.
Recently developed technologies now available are cost effective, require little area, and treat wastewaters to produce water that can be recycled for agriculture, and with minimum treatment, for human use, while also producing valuable fertilizer and fuels. For instance, By recycling sewage effluents as fertilizers on land, producing beautiful gardens, and cutting off sewage nutrients flowing into a bay in Jamaica, the weedy algae that were smothering the reef quickly died (Goreau, 2003). Thirteen years later, the bay is still free of weedy algae, and corals are recovering. These technologies for waste water nutrient and water treatment and recycling are discussed in other chapters of this disc.
The challenge is to mandate and fund use of these methods on a scale that treats all sewage to the point that coastal water is cleaned up and coral reefs and fisheries can recover. Currently, only one country in the world, the Turks and Caicos Islands, requires all developers to build secondary sewage treatment plants and recycle all of their wastewater as irrigation on their own property. Their example needs to be followed by all tropical coastal areas.
INTEGRATED WATERSHED MANAGEMENT
Integrated watershed nutrient management must focus on upstream terrestrial watersheds. Because sewage is only one of several land based nutrient sources, other sources also need to be addressed through this approach (Howarth et al, 2002), which is only in its infancy. Kaneohe Bay, Oahu, Hawaii, where a sewage outfall caused algae to proliferate and kill the reef, demonstrates this need. When the sewage input (known as a “point source” because it entered the water from the end of a single major sewage pipe) to the reef was stopped, algae died back and the reef gradually recovered. Later, with increasing population growth, the watershed was extensively suburbanized, and while the sewage no longer directly affected the reef, increasing road runoff, drains, lawn fertilizer, and golf course fertilizer, which did not enter the sewage collection system, gradually increased nutrient levels in the bay. This caused a new round of algae overgrowth of the reef. Since these “non-point” sources could not be easily controlled, there is now little that can be done except to treat all run-off or ban use of fertilizers. There is now underway an effort to use large vacuum hoses on barges to suck up the algae. However it is likely that these will just grow back as long as the nutrients remain excessive. Whole watershed nutrient management may be the only long-term solution.
To manage watersheds and minimize contamination of the coastal zone, the locations of all sources and sinks of nutrients must be mapped. In general only the largest ones are well known, and natural biogeochemical cycles that consume or create nutrients are very poorly quantified. In the example of the Negril watershed and coastal zone in Jamaica, a detailed study of nutrients was carried out in conjunction with the development of an environmental management plan to reduce nutrient contamination that was killing the reef on which the area’s tourism economy was based,. This covered not only all the reefs and mangroves all around the coast, but also made measurements of nutrients along the length of all the rivers, swamps, wetlands, every spring, and groundwater measured from caves and wells (Goreau & Goreau, 1996).
These data were used as input in a Geographic Information Systems model that digitally mapped the entire watershed’s topography, slope, geology, soil types, habitats, land use, agriculture, and population density (Eirum, 1998; Rybaczuk, 2001). Multiple statistical regressions revealed which combinations of all of these parameters were the major sources, and sinks, of nutrients in the entire watershed and coastal zone. The results showed that all rivers were contaminated by nutrients at the source springs, that these nutrients increased wherever rivers flowed through populated areas (most poor rural inhabitants had no toilets, and used the river to discard their wastes into), and through agricultural land (sugar cane fields were heavily fertilized and ploughed right to the river banks, with no tree barrier). But wherever rivers flowed through intact wetlands, nutrients were absorbed from the water, as fertilizer for wetland plant growth. Unfortunately these valuable natural ecosystem functions were being steadily diminished because wetlands were regarded as “waste land.”. Poor squatters and rich land grabbers alike actively destroyed wetlands, dumping landfill on which to build houses and digging trenches and canals to drain the areas and make way for houses and farms. This converted areas that were once consuming nutrients into areas that added more nutrients to the water, as vegetation and organic wetland peat soils decomposed and released the nutrients they had previously trapped.
Later, the integrated watershed and coastal zone management approach developed in Negril inspired international programs for water quality management called “Ridge to Reef”, “Hilltop to Ocean (H2O)”, and “Whitewater to Bluewater”, Most of these however, focused on symbolic steps of limited impact rather than holistic solutions to manage nutrients on a whole watershed basis. Analytical tools to pinpoint all major nutrient sources and identify where the most effective reduction strategies could be applied were not put into action. Negril was unfortunately an example of such a failure. Despite calls for all the watershed’s sewage to be collected and treated to tertiary level in order to remove nutrients before they entered the reef, foreign aid donor agencies built a sewage collection system that ran down the coastal road, collecting only sewage from tourist hotels and villas along the shore, and ignoring the 90% or more of the watershed’s sewage produced by local residents, mostly in slums, the hills, and the rural interior. The small fraction of sewage addressed was not treated to a level that removed nutrients. Despite warnings that this was a cosmetic plan that could not possibly solve the region’s water contamination problem that was killing the reef, it went ahead. The result was that the reef and fisheries continued to decline.
Ground water inputs present a special problem, especially in highly permeable limestone aquifers, common on most oceanic islands and coral reef coasts. Large amounts of highly nitrate-enriched ground water flows directly into the sea via submarine springs and caves, and there is no practical way to intercept and treat these waters, which flow deep below the surface in mountainous areas. The only practical solution is to minimize contamination at the groundwater sources. In the Negril watershed, for example, all springs were highly contaminated because sink holes in the hills, through which rain water flows into the ground and later emerges from springs in the foothills, were widely used for dumping sewage and garbage, due to the absence of any sanitary or collection facilities (Goreau & Goreau, 1996).
These examples show that the tools for sound, holistic watershed and coastal zone management exist, and could be applied on a large scale to enhance natural processes and protect sensitive habitats, if the will and the funding to do so exist.
NEW TECHNOLOGY FOR IMPROVED COASTAL NUTRIENT MANAGEMENT
Current methods of assessing coastal water nutrient concentrations provide inadequate data to identify nutrient source locations, magnitudes, and changes needed for their management. Sampling is conducted very rarely, sometimes once, sometimes annually, but rarely with a frequency that allows variability to be adequately characterized. Given large variations in rainfall inputs and in tidal, wind, and wave driven water movements around small scale submerged topographic features and shorelines, it is nearly impossible to know where the nutrients came from using such data. Samples for analysis are typically collected large distances apart, due the high cost of analysis, and so spatial gradients, which are often large, are very poorly characterized. Major sources can be completely missed if they lie between sampling locations. Samples are collected and stored, often for a long time, which can result in significant storage and analysis artifacts even if samples are immediately frozen or poisoned to prevent bacterial activity that removes or adds nutrients to the sample.
These problems would be eliminated if a less costly method allowed continuous real time measurements of nutrients to be made. This is routinely done for other water quality parameters such as temperature, salinity, dissolved oxygen, and chlorophyll (from planktonic micro-algae), which can be continuously measured using electrodes from boats. Nutrients cannot be measured by electrodes, since accurate low-level measurements require chemical reagents to be added for each nutrient form, causing a specific color to develop whose intensity is measured by a spectrophotometer. Recent advances now allow nutrient measurements to be carried out continuously, in real time, and on very small volumes. This avoids problems of poor temporal and spatial resolution, eliminating sampling, storage, and analytical artifacts in the data, and at much lower cost. Very small samples, microliters instead of milillters, are analyzed at the same precision, reducing costs of chemical reagents a thousand-fold. Water samples are continuously pumped and reacted with reagent chemicals, and nitrate, ammonium, and phosphate are measured simultaneously by battery powered fibre optic spectrophotometers. Such measurements have been possible for more than 25 years, but have only recently become available in commercial instruments, and only one manufacturer now makes instruments capable of truly continuous operation (www.subchem.com). This allows mapping of nutrients with unprecedented spatial resolution and determination of changes with unprecedented temporatl resolution (Hanson & Donaghay, 1998; Hanson & Moore, 2001; Dickey et al., 2009). Several other instruments are capable of measurements every 15 minutes or so, at lower cost but much less spatial mapping accuracy from a moving boat.
The new instruments have mainly been used by oceanographers, who are usually interested in time series measurements at a single point, usually from moored lines in deep water. Their instruments must be capable of withstanding high pressure, recording data and transmitting it to surface receivers, greatly increasing costs. But instruments without these refinements could be used from small boats to map the distribution of nutrients in surface waters, which is what coastal zone managers need to know. With such instruments a small boat can go all around a small island and locate every single source of nutrients, even those that were not previously known, and track them to their origin. By repeating these tracks around coasts, and onshore-offshore transects, temporal variability can be identified to any desired level of precision, for example sampling after major storms or floods. The same instruments can also be used in rivers and surface waters for whole nutrient watershed mapping as well as in the coastal zone.
Use of the new technology will for the first time take coastal zone and watershed nutrient management out of the dark ages, and allow managers to find all the sources and sinks of nutrients, characterize their magnitudes and variations, design specific management measures to reduce them, and quantify the success of such steps. It is time for coastal zone management to become a quantitative and scientifically sound process rather than the uninformed guesswork it now largely is.
REFERENCES
Anderson, D. M., P. M. Glibert, & J. M. Burkholder, 2002, Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences, Estuaries, 25: 704-726
Backer, L. C., & D. J. McGillicuddy, 2006, Harmful algal blooms at the interface between coastal oceanography and human health, Oceanography, 19: 94-106
Bell, P. R. F., 1992, Eutrophication and coral reefs: some examples in the Great
Barrier Reef lagoon, Water Research, 26: 553-568
Dickey, T., N. Bates, R. H. Byrne, G. Chang, F. P. Chavez, R. A. Feely, A. K. Hanson, D. M. Karl, D. Manov, C. Moore, C. L. Sabine, & R. Wanninkhof, 2009, Advanced sensing for ocean observing systems, Oceanography, 22: 168-181
Eirum, T., 1998, Applicability of GIS as a water quality interpretation tool in the Negril and Green Island Watersheds, Jamaica, Thesis, Trinity College, Dublin, 149 p.
Goreau, M., & T. J. Goreau, 1996, Nutrient sources, water quality, land use, and environmental management of coral reefs, mangroves, wetlands, rivers, springs, aquifers, forests, agricultural lands, and urban areas in the proposed Negril Environmental Protected Area, Jamaica, Global Coral Reef Alliance, https://globalcoral.org/water_quality_in_the_negril_area.htm
T. J. Goreau, T. J., T. Fisher, F. Perez, K. Lockhart, M. HIbbert, & A. Lewin, 2008, Turks and Caicos Islands 2006 coral reef assessment: Large-scale environmental and ecological interactions and their management implications, Revista Biologia Tropical, 56; 25-49 https://globalcoral.org/Turks%20and%20Caicos%20Islands%20Coral%20Reef%20Health%20Assessment.htm
Goreau, T., 2003, Waste Nutrients: Impacts on coastal coral reefs and fisheries, and abatement via land recycling, 28p., United Nations Expert Meeting On Waste Management In Small Island Developing States, Havana, Cuba https://globalcoral.org/WASTE%20NUTRIENTS%20IMPACTS%20ON%20COASTAL%20CORAL%20REEFS.pdf , http://www.sidsnet.org/workshop/experts_meetings.html
http://www.sidsnet.org/docshare/other/20040310124457_case_study_by_Thomas_J_Goreau_on_waste_mgmt_2003.pdf
Goreau, T. J., & K. Thacker, 1994, Coral Reefs, sewage, and water quality standards, Proceedings of the Caribbean Water and Wastewater Association, 3:98-116 https://globalcoral.org/CORAL%20REEFS.%20SEWAGE,%20AND%20WATER%20QUALITY%20STANDARDS.htm
Goreau, T. J., R.L. Hayes, & D. McAllister, 2005, Regional patterns of sea surface temperature rise: implications for global ocean circulation change and the future of coral reefs and fisheries, World Resource Review, 17: 350-374 https://globalcoral.org/WRR%20Goreau%20Hayes%20&%20McAlllister%20.pdf
Goreau, T. J, 2006, Tourism, water quality and coral reefs,
http://www.biorock-thailand.com/tourismwaterquality512.html
Hallegraeff, G.M. (2003). Harmful algal blooms: a global overview, in: Hallegraeff, G.M., G. M Anderson, & A. D. Cembella (Eds.), Manual on harmful marine microalgae. Monographs on oceanographic methodology, 11: pp. 25-49.
Hanson, A. K., & P. L. Donaghay, 1998, Micro- to Fine-scale chemical gradients and layers in stratified coastal waters, Oceanography, 11: 10-17
Hanson, A. K., & C. Moore, 2001, Real time nutrient surveys in coastal waters, Sea Technology, 42: 10-14
Howarth, R, D. Anderson, J. Cloern, C. Elfring, C. Hopkinson, B. Lapointe, T. Malone, N. Marcus, K. McGlathery, A. Sharpley, & D. Walker, 2000, Nutrient Pollution of Coastal Rivers, Bays, and Seas, Issues in Ecology 7: 1-15
Howarth, R., A. Sharpley, & D. Walker, 2002, Sources of nutrient pollution to coastal waters in the United States: Implications for achieving coastal water quality goals, Estuaries, 25: 656-676
Lapointe, B. E., M. M. Littler, & D. S. Littler, 1993, Modification of benthic community structure by natural eutrophication: The Belize barrier reef, Proceedings of the 7th International Coral Reef Symposium, 1: 323-334, Guam
Lapointe, B. E., D. A. Tomasko, & W. R. Matzie, 1994, Eutrophication and trophic state classification of seagrass communities in the Florida Keys, Bull. Mar. Sci. 54: 696
Littler, M. M., D. S. Littler, & B. L. Brooks, 2006, Harmful algae on tropical coral reefs: bottom up eutrophication and top-down herbivory, Harmful Algae, 5: 565-585
National Academy of Sciences, 2000, CLEAN COASTAL WATERS: Understanding and Reducing the Effects of Nutrient Pollution, Committee on the Causes and Management of Coastal Eutrophication, Ocean Studies Board and Water Science and Technology Board, Commission on Geosciences, Environment, and Resources, National Research Council, NATIONAL ACADEMY PRESS, 428 p. Washington, D.C.
Nelleman, C., S. Hain, & J. Alder, 2008, In dead water: Merging of climate change with pollution, over-harvest, and infestations in the world’s fishing grounds, 64 p., UNEP, Nairobi, Kenya
Newell, R. I. E., 1988, Ecological Changes in the Chesapeake Bay: Are they the result of Overharvesting of the American Oyster, Crassostrea virginica?, In Understanding the Estuary: Advances in Chesapeake Bay Research, Chesapeake Research Consortium Publication 129, pp. 536-546. Baltimore.
Nixon, S. W. 1995. Coastal marine eutrophication: A definition, social causes, and future concerns. Ophelia 41:199-219.
Rybaczuk, K., 2001, GIS as an aid to environmental management and community participation in the Negril Watershed, Jamaica, Computers, Environment, and Urban Systems, 25: 141-165
Sellner, K. G., G. J. Doucette, & G. J. Kirkpatrick, 2003, Harmful algal blooms: Causes, impacts, and detection, Journal of Industrial Microbiology and Biotechnology, 30: 383-406
UNEP, 2006, The state of the marine environment: Trends and Processes, 52 p., Nairobi, Kenya
Wade, B. A., 1972, A description of a highly diverse soft-bottom community in Kingston Harbour, Jamaica, Marine Biology, 13: 1432-1793
Wade, B. A., L. Antonio, & R. Mahon, 1972, Increasing organic pollution in Kingston Harbour, Jamaica, Marine Pollution Bulletin, 3: 106-110
NUTRIENT ANALYSIS FOR EFFECTIVE COASTAL ZONE WATER QUALITY MANAGEMENT IN TROPICAL CORAL REEFS
Comments prepared for the Cayman Islands Department of Environment
Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance
April 13, 2025
CAYMAN ISLANDS WATER QUALITY
The Cayman Islands historically have some of the clearest waters in the Caribbean due to the complete absence of rivers dumping mud and sewage into the sea.
Nevertheless, the effects of land-based nutrients are clearly visible as high-nutrient indicating algae overgrowth of reefs wherever nutrients soak into the sea from groundwater and drainage canals.
The sources of nutrients feeding harmful algae blooms in Cayman waters include septic tanks, the sewage plant (which only treats a tiny portion of the sewage the islands produce, and does not treat them to tertiary level to remove nutrients), the garbage dump, the dolphinarium, the turtle farm, sting ray and tarpon fish feeding, golf courses, garden and lawn fertilizers.
With increasing population, increased local nutrient sources risk tipping the reefs over into being totally overrun by weedy invasive algae, as has already happened to Florida, Cancun, Cozumel, Nassau, Jamaica, Barbados, and almost all tourism areas across the Caribbean.
Cayman’s distinctively clean waters and healthy reefs are imperiled unless land-based nutrient inputs causing large-scale ecological changes in the coastal zone are reduced.
This will require establishment of ecosystem-specific coastal water quality nutrient standards for coral reefs, sea grasses, and mangroves, and the means to accurately determine ambient levels to determine if management of nutrient sources meets the desired goals.
NUTRIENT WATER QUALITY STANDARDS
Cayman lacks nutrient water quality standards that protect the health of coral reefs, seagrasses, and mangroves.
The only country in the world that does have coral reef-safe nutrient standards, the Turks and Caicos Islands, lacks the monitoring capacity at the Department of Environment and Coastal Resources needed to enforce its high standards.
However, the TCI islands are drier and lower than the Cayman Islands, and have no nutrient-rich fresh ground water flow to the sea, as much rainier Cayman does.
Almost all water quality monitoring studies focus on use of real-time electrode measuring instruments lowered into the water, but there are no such instruments sensitive enough to measure nutrients accurately at the low levels in coral reefs, indeed the deadly excess thresholds of nutrients in coral reefs are undetectable by conventional water quality monitoring kits, which are widely used to falsely claim reef waters are “unpolluted”!
Those parameters that can be easily measured, such as temperature, salinity, pH, and dissolved oxygen are of little practical use for water quality management since changes in pH and dissolved oxygen are the results of pollution, rather than their real causes: which are excessive nutrients driving the extreme chemical, microbiological, and ecological changes that coastal zone managers most need to monitor and control.
Oxygen (and BOD) values are needed to identify spreading dead zones caused by excessive nutrient inputs, but are almost invariably reported only as oxygen concentrations in ppm, and almost never reported as the much more useful oxygen percent saturation at ambient temperature and salinity, which allows coastal ecosystems to be accurately characterized as net producers or consumers of oxygen and carbon dioxide (autotroohic or self-feeding, versus heterotroohic or based on decomposing food produced elsewhere) the most critical parameters of overall ecosystem health.
NEAR REAL-TIME NUTRIENT MAPPING
Until water quality monitoring provides accurate real time mapping of nutrients, coastal zone managers will be in the dark on the effects of water quality management.
The low levels of nutrients in healthy coral reefs, and the rapid rates at which nutrients are consumed or released, cause storage artifacts in water samples that can only be prevented by near real-time in-situ measurements using spectrophotometry of nutrient chemical reaction products.
Such instruments are now available that are portable, battery operated, can be deployed from small boats, and can make complete measurements of nitrate, nitrite, ammonium, and phosphate in around 5 minutes on tiny samples only a few microlitres in volume, pumped through small volume peristaltic pumps to minimize analytical chemical use cost and pollution. Such an instrument allows mapping of coastal zones that lets every nutrient source be tracked to its origin, and confirm if management efforts to reduce nutrient inputs have the required effects.
It is recommended that the Cayman Islands Government establish coral reef-specific water quality standards of 1 micromole per litre of nitrogen (ammonium, nitrate, plus nitrite) (0.014 ppm) and 0.1 micromole per litre of phosphorous (orthophosphate plus dissolved organic phosphorous) (0.003 ppm), and establish a portable nutrient measuring laboratory to map changes in nutrients in Cayman coastal waters on seasonal, extreme event, and long term scales.
An example of such an instrument is at:
https://www.systea.it/en/our-products/portable-analyzers/
NB This is for information only: I have no connection at all to the manufacturer, but this is the instrument I would probably choose based on quality and price unless a more suitable one can be found.
BACKGROUND INFORMATION:
The applications of near real-time water quality monitoring for coastal zone managers is explained in:
T. Goreau, 2009, Integrated nutrient management of coastal waters and watersheds, 10p., in T. J. Goreau & S. T. Nielsen (Eds.), The Green Disc: New Technologies for a New Future, Gibby Media Group, Spokane WA
(attached).
For background information on coral reef nutrient thresholds see:
T. J. Goreau & K. Thacker, 1994, Coral Reefs, sewage, and water quality standards, PROC. 3D. CARIBBEAN WATER AND WASTEWATER ASSOCIATION CONFERENCE, WATER AND WASTEWATER NEEDS FOR THE CARIBBEAN: 21ST CENTURY, Kingston, Jamaica, 3:98-116
T. Goreau, 2003, Waste Nutrients: Impacts on coastal coral reefs and fisheries, and abatement via land recycling, 28p., UNITED NATIONS EXPERT MEETING ON WASTE MANAGEMENT IN SMALL ISLAND DEVELOPING STATES, Havana, Cuba
A. DeGeorges, B. Reilly, & T. Goreau, 2010, Land-sourced pollution with an emphasis on domestic sewage: Lessons from the Caribbean and implications for coastal development on Indian Ocean and Pacific coral reefs, Sustainability, 2: 2919-2949
Bell, P.R., Elmetri, I. and Lapointe, B.E., 2014. Evidence of large-scale chronic eutrophication in the Great Barrier Reef: quantification of chlorophyll a thresholds for sustaining coral reef communities. Ambio, 43, pp.361-376.
